Atomic KMS: enable bypass

[tarek-y-ismail]

Apologies for the general suckiness of the code, will improve that once it actually works.

[RAOF]

This is where the problem lies; drmModeAddFB2 expects GEM handles, and you're giving it dmabuf file descriptors.

Here is the necessary DRM API for converting the two, along with an ominous warning about the sharp edges of that API.

Since I think we share the underlying FD with the RenderingPlatform (and so with EGL etc), I think we'll need to do the “everything goes through gbm” route. That means going through gbm_bo_import (with type = GBM_BO_IMPORT_FD_MODIFIER and flags = GBM_BO_USE_SCANOUT) and then pulling all the GEM handles out with gbm_bo_get_handle_for_plane (and then handling the lifetime of the gbm_bo, keeping a track of it, and destroying it when necessary)